196 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



with a furrow interrupting these ribs on the abdomen, often 

 forming a pair of shoulder keels. The septum is finely and 

 deeply divided; in addition to the first and second lateral 

 lobes there are one or more auxiliary lobes, and the two 

 lateral saddles are deeply divided by secondary lobes. 



This genus, which Neumayr supposed to have originated 

 from Peris^hiiictes, included many species that have since 

 been placed in other genera, in some cases even in other 

 families, but after the segregation from it of Sonneratia 

 Bayle, Sioliczkaia Neumayr, Pulchellia Uhlig, there is still 

 left a large number of species, showing great variation in 

 form and other characters, which may, after all, not belong 

 to a monophyletic genus. Zittel (1885, p. 475 ; 1895, p. 428) 

 first classed Hoflites with the Stephanoceratidas ; then in a 

 later work, with the Cosmoceratidae, along with Cosmoccras 

 Waagen, Parkinsonia Bayle, Sonneratia Bayle, and Acan- 

 thoceras Neumayr, as a side branch from the Stephanocera- 

 tidcE. Zittel is inclined to the belief that Cosmoceras is the 

 direct ancestor of Hopliies, an opinion which seems to be the 

 more correct, for the two species of Placenticeras, of which 

 the ontogeny is described in this paper, show a decided Cos- 

 moceras stage in the adolescent period just before the Hojylites 

 stage, and one of them retains some of these characters 

 until maturity. In each case this stage begins by a sudden 

 stopping of the perisphinctoid ribs on the abdomen, the 

 formation of strong knots on the angular abdominal shoul- 

 ders, and a sharper forward bending of the lateral ribs, 

 which fork near the shoulders, forming the beginning of a 

 second row of knots. At this stage one can see a resem- 

 blance, not to the exaggerated species of Cosmoceras, such 

 as C. ornatum, C. jason, or C. elizahethcB, but rather to 

 some simpler form ; it is not possible to refer to any partic- 

 ular species as the ancestral form, nor is it likely that any 

 one species was the only one that developed the style of 

 rough ornamentation that is called Hopliies. 



F. Bernard ( 1895, p. 673) agrees substantially with Zittel as 

 to the systematic position of the genus, as do also most other 

 writers on the subject; Steinmann (1890, p. 445) groups it 



